Function reference ambiguous

Question

Why does a compiler error occur stating that my links are ambiguous? I have float , int and string that should create separate function signatures, right?

Here is what I still have:

 #include <iostream> #include <string> using namespace std; int plus(int a, int b); float plus(float a, float b); string plus(string a, string b); int main(void) { int n = plus(3, 4); double d = plus(3.2, 4.2); string s = plus("he", "llo"); string s1 = "aaa"; string s2 = "bbb"; string s3 = plus(s1, s2); } int plus(int a, int b) { return a+b; } // int version float plus(float a, float b) { return a+b; } // float version string plus(string a, string b) { return a+b; } // string version 

Answer 1

First, do not use using namespace std; . In this case, there is a structure called std::plus -oh, wait, no matter what is actually called plus and its constructor is thrown into the bucket to allow overloading using the plus function.

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Secondly, you have ambiguity, because 3.2 and 4.2 are of type double and can convert equally well to float or int .

This is a simplification, but when it comes to passing numbers to an overloaded function, C ++ basically uses these rules:

• If all arguments exactly match one of the overloads, use this one.
• If all arguments can be raised to fit one of the overloads, use this one.
• If all arguments can be numerically converted to match one of the overloads, use this one.

If you have several candidates at a certain level, then this is ambiguity. Rarely, a double does not advance to float , which would be a drop. Therefore, it should use the standard conversion in float , which is associated with the standard conversion with int , so these two overloads are ambiguous.

Answer 2

Call float overload as follows:

 double d = plus(3.2f, 4.2f); 

A constant like 3.2 does have a double .